When performing tandem mass spectrometry, or MS/MS on a mixture of ions of unknown mass, there are a few approaches that have been attempted in the past. For example, a survey scan can be performed on precursor ions, and mass peaks of interest can first be identified, prior to selecting and fragmenting precursor ions. This can be characterized as an information dependent acquisition (IDA) method. However, this method can miss small peaks or components that are not identified as being of interest in the survey scan, and it can be inefficient if a large population of precursor ions is present, because it may be necessary to re-analyze the sample in order to identify all of the components. Alternatively, a mass filter can scan over a mass range of interest and acquire MS/MS on every precursor ion. This can be characterized as an MS/MS of everything method. While this avoids the need for survey scans and does not require any decisions about which precursor ions to select for MS/MS it is inefficient and slow, especially when the mass range of interest is large, as again significant amounts of sample are wasted. In a simple example, if the mass range of interest for a sample is 300 to 1000 amu, and the mass filter that selects the precursor ion has unit mass resolution (a peak width of approximately 1 amu), then MSMS spectra can be acquired in 1 amu steps from m/z 300 to 1000. Since most samples are analyzed by LC/MS, this requires acquiring 700 MS/MS spectra every few seconds, or even every second, sufficiently fast that at least one, and preferably more than one, complete MS/MS of everything acquisition is performed during each LC peak.